Process for preparing a vitreous carbon

ABSTRACT

The process for producing a vitreous carbon involves the molded product of a moldable composition produced from co-reacted mixtures of powder or otherwise blendable form of 20-80% by weight of a phenolic-furfuraldehyde Novolac resin and of 20-80% by weight of phenolic-aldehyde resol resin dispersed in water, either in solution or suspension, the percentages being based on the combined weight of the Novolac and resol resins, and the aldehyde in said Novolac resin comprising at least 50 molar percent, preferably substantially 100 percent, furfuraldehyde. The composition advantageously contains an amine such as hexamethylenetetramine (&#34;hexa&#34;) in an amount equivalent to 1-15%, preferably 2-10% of hexamethylenetetramine based on the total amount of phenolic component. The composition is made by adding the preformed phenol-furfuraldehyde Novolac to the resol resin prior to dehydration of the resol resin to produce a grafted polymerization product of improved properties. The composition is particularly useful in admixture with a carbonaceous filler, preferably graphite in a proportion as high as 76% by weight based on the total composition. Generally in such admixtures the graphite may comprise 30-76%, advantageously 35-65% and preferably 40-60% of the molding composition. The vitreous carbon is improved in electrical properties and in the capability of being suitably molded, carbonized and graphitized into large shapes, particularly thin plates which are much more stress-free and crack or pore-free than otherwise produced.

This application is a continuation-in-part application of copendingapplication Ser. No. 06/668,396 filed Nov. 5, 1984, now abandoned, whichis a continuation of application Ser. No. 502,181, filed June 8, 1983,now abandoned, which in turn is a continuation-in-part of applicationSer. No. 356,893 filed Mar. 10, 1982, now abandoned, which in turn is acontinuation of application Ser. No. 182,755 filed Aug. 29, 1980, nowabandoned, which in turn is a continuation-in-part of application Ser.No. 050,531 filed June 21, 1979, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to new vitreous carbon compositions derived fromthe addition of a phenol-furfuraldehyde Novolac to a phenol-aldehyde"resol" resin. More specifically, it relates to the production ofvitreous carbon in large, molded sizes, particularly large thin platesproduced by appropriately compressed and molded shaped articles whichare carbonized and then graphitized to excellent vitreous carbon withlow percentages of failures or rejects. Still more specifically, itrelates to a process for making such vitreous carbon products.

2. State of the Prior Art

The extreme inertness and non-porosity of vitreous carbon qualifies itas an important and useful material of construction for use in a numberof applications and in various industries. For research and developmentwork this material has been used in fabricating beakers, basins, boats,reaction tubes, etc., and for extensive use in the processing ofsemiconductors, fluoride laser materials, zone refining of metals, zonerefining of chemicals, biomedical applications, fuel cell electrodes,etc.

However, industrial applications of vitreous carbon have been made onlyin recent years. Since vitreous carbon is not wet by a wide range ofmetals including zinc, silver, copper, tin, lead, aluminum, gold,platinum and others, it has found application in the processing of someof these metals and their alloys, for example, in the dehydrogenation ofmolten aluminum with chlorine gas. Dip pipes of this material forcorrosive liquids have also been successfully used.

The growth of industrial applications for this material has beenrestricted in large measure by the inability to produce properly curedmoldings or extrusions in the required shapes and by use of conventionalmolds or dies at conventional rates and reasonable cost. There has beendifficulty in making large thin plates suitable for use in fuel cells.

A "resol" resin is the resinous reaction product of a phenol and analdehyde which has been condensed (reacted) only to a stage where itstill melts when heated and is still soluble in acetone, and the resinstill has sufficient residual reactivity that it may be cured by heatwithout the addition of a curing agent to an insoluble and infusiblecondition. A resol resin is also known as an "A" stage phenolic resin,or also as a "single stage" resin, because it is curable without theaddition of any crosslinking agent.

The "resol" resin is prepared by using the aldehyde in a molarproportion greater than 1-1 with the phenol. Since sufficient aldehydeis already present to give a cure to the insoluble, infusible state,there is no need to add a curing agent such as hexa for final curing.However, in preparing the resol resin, it may be desirable to add asmall amount of hexa to obtain a harder and more easily grindable resol.For example, 0.005 to 0.03 mole, preferably 0.01 mole of hexa per moleof phenol is advantageous for this purpose. In any case, the amount ofhexa used in preparing the resol is not calculated in the amount whichmay be subsequently added to aid in the curing of the Novolac-resolmixture.

In contrast, a "Novolac" resin is one prepared with a deficiency inaldehyde so that it may not be cured unless a curing agent such as hexais added. Therefore, a "Novolac" resin may be defined as the resinousreaction product of a phenol and an aldehyde that, for all practicalpurposes, does not harden or convert to an insoluble, infusiblecondition upon heating, but remains soluble and fusible.

In starting with resin particles as described in said pendingapplication, it has been found particularly important that the Novolacis a phenolfurfuraldehyde resin. When the Novolac is one usingfurfuraldehyde, pressures are suitable for compressing the resin mixtureinto the desired shapes for molding which are not suitable for Novolacsmade with other aldehydes. As shown hereinafter, this becomes evident inthe number of rejects produced when the molded objects are carburized tovitreous carbon.

In the parent applications, Ser. Nos. 182,755, 356,893 and 502,181, anumber of references were cited with respect to coreaction of Novolacand resol resins. These include U.S. Pat. Nos. 3,998,906, 3,927,140,3,879,338, 3,410,718, Japanese Patent No. 53-75294 and British PatentNo. 1,090,029. While these references relate to curing various mixturesof resins, none of these pertain to water removal from the variousmixtures so as to produce a moldable composition, particularly one whichmay be subsequently mixed with a carbonaceous filler such as graphitefor further processing into vitreous carbon products.

SUMMARY OF THE INVENTION

In accordance with the present invention, it has been found that resincompositions of excellent molding plasticity may be prepared by adding20-80 percent by weight of a phenolic-furfuraldehyde Novolac resin to anaqueous solution or suspension of 20-80 percent by weight of aphenolic-aldehyde resol resin, preferably in the early stage offormation of the resol resin; the percentages being based on thecombined weight of the two resins, together with an appropriate amountof an amine, such hexamethylenetetramine ("hexa"), the hexa and theNovolac resin being added separately or simultaneously to the resolresin prior to completion of dehydration or water removal from the resolresin. The hexa may be added all in one amount or in two or moreincrements anytime up to removal of 90% of the water, preferably beforeremoval of 75% of the water. The Novolac may be added advantageouslyafter the resol components have been reacted for about 30 minutes atabout 90° C. and advantageously before any substantial amount of waterhas been removed. In preparing the Novolac which is to be added to theresol, at least 25 percent of the water present during the Novolacpreparation is removed, advantageously after at least 35 percent andpreferably at least 50% or 75% of the water has been removed, and stillmore preferably after substantially all of that water has been removed,prior to the Novolac addition to the resol. The preferred ratios ofparts by weight of Novolac to parts by weight of resol prior toco-reaction are in the range of 30/70 to 50-50, or reversely the ratioof parts by weight of resol to parts by weight of Novolac is in therange of 50/50 to 70/30.

In referring to the "removal of water" in a resin or in the formation ofthe resin it is intended to include water present in a component, suchas water in aqueous formaldehyde, or in aqueous caustic solution, etc.,water added as such, and water formed by the resin condensationreaction. The amount of water may be easily determined by first runninga reaction in which water is completely removed. Then subsequentreactions may be performed in which only portions of the water areremoved.

In place of hexa there may be used various amines as described morefully hereinafter. The hexa, or other amine, serves two functions. Firstit serves to harden the resol component and to prevent prematuregelation and also serves to avoid premature gelation when the Novolac isadded. The avoidance of premature gelation is important in permittingcomplete removal of water from the mixed reaction product to give agrindable product that may be subsequently cured in a moldingcomposition.

Advantageously an appropriate amount of hexa is added to the componentsfor the resol, or preferably after the refluxing of the resol componentshas been conducted to a stage where the formaldehyde is substantiallyall reacted or may be added anytime before or after the Novolac is addedand up to the time 90 percent of the water initially present has beenremoved, preferably before 75 percent of the water has been removed.

The amount of amine is advantageously equivalent to 1-15 percent byweight, preferably 2-10 percent by weight of hexa based on the totalweight of phenolic component. Also based on the total weight of resinproduct, the amine is advantageously equivalent to 0.5 to 6%, preferably1 to 5 percent by weight.

After the hexa and Novolac addition are completed, the dehydration orwater removal is continued to a stage where a grindable resin isobtained upon cooling the reaction mass. The resin product has a moldingplasticity particularly suitable for giving excellent flow forcarbonaceous-filled, such as graphite-filled, molding compositions whichare particularly suited for graphitization to produce stress-free andpit and pore-free vitreous carbon.

In curing a Novolac resin, a substantial amount of a curing agent isused such as hexa to overcome the deficiency of aldehyde-bridginggroups. This added curing agent may be an aldehyde such as formaldehydeor an alkylene-providing compound, such as hexamethylenetetramine whichprovides methylene groups for curing. However, when a substantial amountof such a curing agent is used in preparing a cured Novolac resin forultimate vitreous carbon formation, there is generally sufficientby-product gas formed or retained so that in the later stages of theresin processing, molded-in stresses may be formed. In any case, theproducts do not have the properties desired.

By the composition and process of this invention, it has been foundpossible to prepare resins for ultimate formation of vitreous carbon ofvery good properties by virtue of the fact that at least most orsubstantially all of the final bridging between phenolic groups iseffected through methylol groups present in the resol rein to produce aresin of excellent molding plasticity. Thus the necessity for adding acuring agent to the ultimate product to provide bridging groups for theNovolac molecules is eliminated or reduced. The carbonizable phenolicresin produced from the composition of this invention is the coreactionproduct of a phenolic-furfural Novolac resin and a resol resin plus theadded hexa. Some of this co-reaction may take place during thedehydration of the resol.

This co-reacted resin product has a plasticity that makes itparticularly suitable for mixture with finely divided carbonaceousfillers such as graphite to give products having molding plasticitysatisfactory to give molded products of less stress and strain which, inturn on graphitization, gives vitreous carbon products of excellentproperties, free of pits and pores and sufficiently free of cracks andmicrocracks to reduce and practically eliminate rejection of the samefor rupture or failure of permeability tests to determine suitability ofthese for separator plates in fuel cells.

It is believed that the phenol furfural Novolac has a plasticizingeffect on the co-reacted resol resin which allows the resultant viscousmass to flow uniformly and readily at lower pressure to completely fillthe mold before a high degree of gelation and crosslinking occurs. Thiscontrasts with the initially faster curing rates of the single stageresins (resols) which create large initial portions of gelled orcrosslinked polymer molecules, thereby also forming local stressed areasin the molded part. This plasticizing effect is believed to allow theproduction of molded shapes and forms which are substantially free ofmolded-in stress. This allows the formed product to be ejected from ahot mold without distortion or deformation. Moreover, when the moldedproduct is carbonized to vitreous carbon, this stress-free conditioncarries over into the final product to produce excellent propertiestherein.

While mixtures of finely divided preformed phenol-furfuraldehydeNovolacs (PFUN) and finely divided preformed phenol-aldehyde resols(PFR) have been found effective by the process of applicants'above-mentioned prior application Ser. No. 50,531 in the preparation ofotherwise difficult to form vitreous carbon shapes, it has now beenfound that compositions effective for this purpose can be prepared byadding a preformed phenolic-furfuraldehyde Novolac resin to a solutionof phenol-aldehyde resol resin polymerized to a stage in which theproduct has not been substantially dehydrated. The Novolac resin can becompletely dehydrated prior to such addition or may be preformed butstill in the undehydrated stage.

A particularly difficult shape to mold, carburize and graphitizeeffectively is a plate having a molded and ultimate thickness of0.04-0.05, preferably about 0.045". Vitreous carbon plates of thisthickness and with other appropriate dimensions, such as about20-25"×25-30" and even as high as 50"×50" if impervious to gas andliquids, are useful in fuel cells. By the methods disclosed in theabove-mentioned application, applicants have improved the impermeabilityof such plates as would not be obtained without applicants' technique.When any depressions or cracks run completely through the plate, theplate is made permeable and must be rejected. The improved technique ofblending the resins before dehydration and co-reacting the resins duringdehydration produces products with excellent impermeability even withthicknesses of 0.045 inch. With this eliminated and thereby the cost ofacceptable plates reduced.

Gel permeation chromatogram and carbon-13 nuclear magnetic resonancespectrum show that in the blend effected prior to dehydration there is aslight decrease in the molecular weight of the high molecular weightportion of the PFUN and there is a grafting of low molecular weightmaterial to the PFUN. This low molecular weight material is believed tobe low molecular weight hydroxymethylphenol and bis(hydroxmethyl)phenol.

FIG. 1 represents two gel permeation chromatogram curves superimposed oneach other. Curve A represents the gel permeation chromatogram of amixture effected with preformed PFUN and PFR particles according to theprocedure of application Ser. No. 50,531. Dotted Curve B is a gelpermeation chromatogram of a blend effected by adding the same PFUN to asimilar PFR as used for Curve A but prior to dehydration of the same aseffected by the procedure described below in Example V, but adding 35parts of PFUN per 65 parts of PFR. Proportions and other conditions areas identical as possible. Curve B shows a hump at the left side of thehigh molecular weight curve at the left. This is believed to representthe grafting of material as discussed above.

The carbon-13 nuclear magnetic resonance spectrum reflects the graftingphenomenon by a reduction in free hydroxymethyl group resonance at 58-60ppm and changes in the substitution pattern of the phenolic group asshown by the resonance in the range of 152-157 ppm.

Novolac and resol resins may be prepared by the condensation of a largevariety of phenols and aldehydes as described in "The Chemistry ofSynthetic Resins" by Carleton Ellis, Vol. 1, page 315, ReinholdPublishing Co., N.Y., N.Y. (1935). The author describes numerousphenolic-aldehyde resins in Chapters 13-18, modified phenol-aldehyderesins in Chapter 19, and modified phenol-formaldehyde resins in Chapter20.

Typical examples of the phenolics which may be used are: phenol itselfand its various homologs such as meta-cresol; the various xylenols,hydroquinone, pyrogallol; resorcinol; the halogenated derivatives ofphenol which leave two or more positions available for condensation withthe aldehyde, such as p-chlorophenol, p-bromophenol, p-fluorophenol,etc.; the various naphthols, the various hydroxy-benzoic acid esters;p,p'-dihydroxydiphenylmethane;p,p'-dihydroxydiphenyl-2,2'-diphenylpropane, etc. Ortho- and para-cresolmay also be used when mixed with another phenol, such as metal-phenol,which has three available reactive positions such as ortho and para topermit crosslinking. For economic and availability reasons, phenolitself is preferred.

Similarly, a wide variety of aldehydes may be used in preparing theresol resins for use in the present invention. Typical examples areformaldehyde, paraformaldehyde, acetaldehyde, butyraldehyde, glyoxal,acrolein, benzaldehyde, terephthaldehyde, etc. Again, for reasons ofcost and availability and for ease in processing, formaldehyde ispreferred. The term "aldehyde" is intended to include not only aldehydesper se, that is compounds containing the --CHO group, but also compoundswhich, under reaction conditions, can engender an aldehyde or providethe same type of alkylene group for bridging as provided by thealdehyde. For example, hexamethylenetetramine provides methylenebridging groups, and acetylene under appropriate conditions with phenol,produces resins similar to those produced from phenol and acetaldehyde.

The appropriate molar ratio of aldehyde to phenol for preparing theNovolac and for preparing the resol respectively depends upon the natureof the aldehyde and the nature of the phenol and the conditions underwhich they are reacted.

With furfuraldehyde (furfural) as the condensing aldehyde for theNovolac, the proportion is advantageously in the range of about 0.6-0.9,preferably about 0.70-0.75 mole per mole of phenol. The furfural may beadded all at once or in two or more stages.

The primary requirement is that the Novolac conforms to the accepteddefinition of a Novolac, namely that the phenolic-aldehyde resin willnot cure merely upon heating and therefore for all practical purposes,is not heat-convertible to an insoluble, infusible product.

A further requirement of the Novolac is that it must be capable ofconversion to an insoluble, infusible product by heat reaction withadded amounts of an aldehyde, such as formaldehyde or an aldehydereactive type of compound such as hexa. (See Ellis as cited above, p.327.) Thus the Novolac may be tested by the addition of 10% by weight ofhexa and heated. A true Novolac will be cured to an insoluble, infusibleresin. If the material is not so cured upon testing, an additionalamount of hexa may be added and the test repeated. If still no cure, thematerial is definitely not a Novolac. For use in the practice of thisinvention, the Novolac must meet this curing test to insure that it willbe capable of curing with the resol to an insoluble, infusible state.

Thus in the practice of this invention most of the crosslinking bridgesof the Novolac are formed by the resol. The hexamethylenetetramine addedwith the Novolac supplements the crosslinking bridges formed by theresol. However, the amount of hexa may be an amount that will producethe desired effect but still be low enough to avoid the disadvantagesdescribed above. As indicated above, this amount is advantageously 0.12to 12 or preferably 2 to 8 parts by weight per hundred parts of theweight of Novolac resin.

As indicated above, various amine may be used in place of the hexa toperform a similar function. These amines include ammonia and any aminehaving a free hydrogen attached to the nitrogen atom such as mono anddialkylamines, e.g., methylamine, dimethylamine, ethylamine,diethylamine, butylamine, dibutylamine, decylamine, etc., mono anddiarylamines such as aniline, diphenylamine, benzidine,methylendianiline, etc., monoaryl-monoalkylamines such asN-methylaniline, N-ethylaniline, N-propyl-tolylamine, etc.Advantageously the hydrocarbon groups have between 1-21 carbon atomspreferably 1-10 carbon atoms.

Resols are prepared from phenols and aldehydes over a wide molar ratioof reagents depending on the particular phenol and particular aldehyde.In this case also, a generalization can be made when the phenoliccompound is phenol and the aldehyde is formaldehyde. Phenol-formaldehyderesols are usually prepared under alkaline or basic conditions, or inthe presence of metal salts such as zinc acetate, to give resinouscondensation products having a number of unreacted methylol groups aswell as methylene bridges, both derived from the aldehyde. The ratio offormaldehyde to phenol varies for resols, preferably from a ratio of1.05/1 to 1.5/1. In some formulations, some of the bridging groups maybe supplied by hexa.

The available methylol groups in the resol are likewise the activefunctional groups which coreact with the Novolac to effect bridging andthereby produce the thermoset resin used in subsequent carbonization toproduce vitreous carbon.

In preparing the furfural-phenol Novolac, an alkaline catalyst ispreferred to obtain a controlled condensation. An acid catalyst isavoided since the acid is likely to initiate additional polymerizationthrough the ethylenic unsaturation in the furan ring, which has a cyclicdiene-ether structure.

In contrast, when producing a Novolac with furfural under alkalineconditions, such as with sodium carbonate, a furfural-to-phenol molarratio of 0.60/1 to 0.90/1, preferably 0.70 to 0.75, produces a Novolacwhich upon normal heating will not cure, but will do so upon theaddition of formaldehyde or hexa. However, if an acid is present duringthe initial condensation or is added thereafter, the resin can undergoadditional reaction which may be misinterpreted and the resin consideredto be resol in character. For example, if a furfural Novolac is treatedwith a strong acid, a vinyl-type addition reaction will be promoted andthe resultant additional polymerization will effect bridging betweenpolymer molecules.

The carbonized resins of this invention are suitable for use aselectrodes in electrochemical systems, such as in chlorine cells; inmolten aluminum systems; in electroplating systems; in direct electricalgenerating systems using strong electrolytic acids such as sulfuric andphosphoric acids together with methane and air, hydrogen and oxygen orchlorine, etc. as fuels; as Barnes capture devices or control rods innuclear reactors; in aerospace systems; as support or walls in catalyticsystems; as metallurgical crucibles; diffusion sheets or plates indiffusion devices; as zone refining units, etc.

The production of formed shapes from the Novolac-resol co-reactedcompositions of this invention is achieved by well known techniques,such as by compression, injection, transfer and impulse molding. In eachcase, the resin mixture is introduced into a hot mold under pressure atleast sufficient to force the mixture to fill all parts of the mold, andthe resin mixture is cured to an insoluble, infusible state.

The temperature used will vary over a wide range, depending on thecomposition of the Novolac and the composition of the co-reacted resol,the presence or absence of added furfural as either an externalcrosslinking agent or a reactive plasticizer, the amount and type ofcarbonaceous fillers and other non-gassing fillers, etc. However, mostof these compositions can be molded in the range of 100° to 166° C.(212° to 330° F.) but in some cases temperatures as 180° C. (356° F.)may be used. The preferred range is 149°-166° C. (300°-330° F.).

The same factors recited above as effecting the molding temperaturesused as well as the temperature itself, in many cases also affect thechoice of pressure used in molding to a shaped form. However, a higherpressure is required to mold a blend containing 60% graphite filler thanfor one containing 40% or 20% or 0% graphite.

Moreover, the shape of the molded part will also influence the selectionof a suitable molding pressure which may require one pressure forcompression molding and a higher pressure for transfer molding, and astill higher pressure for injection molding which can be at 20 tons persquare inch for transfer and 5 tons per square inch for compressionmolding. The general range of pressures lies between 0.25 to 25 tons persquare inch, and the preferred ranges are 0.25-20 tons per square inchand 0.4-5 tons per square inch for compression molding.

Extractability tests on the molded products of this invention show thatthere is less than 2 percent and generally less than one percent ofmaterial extracted by acetone based on the resin content of the productprovided there is no non-reactive additive present, such as aplasticizer. In fact, in most cases the molded product has very littleextractible material even when strong solvents, such asdimethylformamide, are used. The extractability tests are performedaccording to ASTM Procedure D494-46.

The weight ratio of the respective Novolac and resol resins prior toco-reaction, as well as the presence or absence of various additives ormodifiers such as external curing agents, e.g., hexa, reactiveplasticizers such as furfural, processing aids such as moldingplasticizers, e.g., zinc stearate or stearyl alcohol and various typesof fillers such as graphite, etc., will depend on the application forwhich the vitreous carbon is to be utilized. As discussed herein, theapplications for the products of this invention are extremelydiversified, such as for chemically resisting piping and equipment, andwalls and electrodes for fuel cells, etc.

For most applications, the PFUN:PFR ratio can be from 80:20 to 20:80. Anamine, such as hexa, is added as described above in an amount equivalentto 1-15%, preferably 2-10% of hexa based on the total amount of phenoliccomponent, or 0.5-6%, preferably 1-5% based on the total weight ofresin. As indicated, equivalent amounts of various other amines may beused in place of the hexa. Also 0-5 parts by weight of furfural per 100parts by weight of resin may be added to aid in plasticity.

Mold lubricants may be incorporated in the resins. Suitable lubricantsinclude fatty acids of 14-22 carbon atoms, their esters of alcoholscontaining 1-22 carbon atoms and their metal salts, such as Ca, Zn andMg salts. Typical of these which may be used are oleic acid, stearicacid, Montan wax, stearyl stearate, glyceryl monoleate, glycerylmonostearate, the commercial wax sold under the brand name "Acrawax",zinc, calcium and magnesium stearates, etc. For biomedical applications,the lubricants should be free of metals and metallic compounds. Thelubricants may be used in proportions of 0.5-3 percent by weight basedon total resin composition.

A very useful class of fillers comprises carbonaceous fillers for whichvitreous carbon itself exhibits high adhesion. Such materials includepyrolytic graphite; the normal graphites such as that formed of flat,parallel lamellae of carbon held together by van de Waal's forces(distance approximately 3.35 °A); carbonized celluloses, etc. Foreconomic reasons, the regular graphites generally find greater use invitreous carbon than the other fillers.

In general, with regular graphite as a reference, the proportion of suchfillers in ready-to-use molding powders of this invention may be aslittle as 5% to produce a noticeable effect, but is advantageouslybetween 35 and 65%, preferably about 40-60% by weight of the moldingcomposition. By adjusting the amount of Novolac in the mixture togetherwith the use of hexa, lubricants, furfural, etc., the proportions ofgraphite may be adjusted to 30 to 76% of the molding composition.However, the compatibility of the graphite may be improved by the use offiner grades of graphite as compared to more coarse grades. In somecases, it is desirable to use a combination of varying fineness orcoarseness in the graphite. The use of varying fineness in the particlesize of the graphic enhances the compactness and density of the mixture.For example, in a preferred mixture, the maximum particle sizepreferably does not exceed 300 microns with some particles being in the60 to 160 micron range and some particles being less than 60 microns insize. Similar considerations apply to the other carbonaceous fillers.

The amount of carbonaceous filler can also be expressed as parts per 100parts of the weight of resin. Thus the moldable compositions of thisinvention comprise a heat curable, pressure moldable blend of 80-20parts by weight of the Novolac and 20-80 parts by weight of the resolbefore co-reaction with the combined weight of Novolac and resoltotaling 100 parts by weight, plus 0-230, preferably 0-150 parts byweight of a carbonaceous filler, 0-5 parts by weight of furfuraldehyde,0.5-6 parts by weight, preferably 1 to 5 parts by weight of hexa, and0-3 parts by weight of mold lubricant, with the proportion of each ofthe additives being based on 100 parts by weight of the combined Novolacand resol. With extreme dispersion methods such as ball-millingcarefully to extremely fine particle size, the amount of graphite mayexceed somewhat the amount defined above.

A typical graphite composition may be comprised as follows: 60%graphite, 22.1% phenol-formaldehyde resol co-reacted with 13.0%phenol-furfural Novolac, 1.48% hexa, 0.6% stearyl stearate, 1.25% zincstearate and 1.25% furfural. Another typical composition may comprise:40% grpahite, 34.75% phenol-formaldehyde resol co-reacted with 20.17%phenol-furfural Novolac, 0.1% stearyl stearate, 1% zinc stearate and0.6% furfural. The percentages are percent by weight based on the totalcomposition.

Another typical graphite composition containing 49.9% by weight ofgraphite, 29.2% PFR co-reacted with 16.6% PFUN, 1.9% hexa, 0.4% stearylstearate, 1.0% zinc stearate and 1.0% furfural, after being transfermolded as described herein, is ground and tested for acetone solublecontent. An average of these tests show 0.48% soluble material whichanalyzes to show a mixture of stearate plasticizer and unreactedfurfural.

In special applications, finely dispersed pyrolytic graphite may bepreferred as a filler over normal graphite because of its anistropicproperties which appear to enforce the vitreous carbon with its uniquethermal and mechanical properties. Pyrolytic graphite is purecrystalline graphite deposited from carbon-bearing vapor at temperaturesin excess of 2000° C.

When pyrolytic graphite is used as a filler in the compositions of thisinvention, it appears that vitreous carbon has increased regions ofgraphite (or diamond) crystallinity which are dispersed among the smallstacks of graphite-like layers. The reason for this is not clear, but itis probably due to a nucleating effect. To some measure, this allowssome variability in the ratio of the small stacks of graphite-likelayers interspersed with the regions of graphite crystallinity.

The co-reacted blends of this invention are converted to vitreous carbonby the intermediate steps of molding and curing the shaped form.Adequate cure, and therefore curing temperature and time, are ofparamount importance since undercured articles usually crack during thecarbonization process. The extent of cure may be checked by determiningthe amount of acetone extractable material. Satisfactory products areobtained when the acetone extractable value is no greater than 2percent, preferably less than 1 percent, as determined by ASTM MethodD494-46 based on the weight of resin content.

Many methods of molding may be used. As previously indicated, the formedprecursor part may be compression, transfer, extrusion or injectionmolded. High production volumes are readily obtained with the blends ofthis invention by transfer and injection molding in a multicavity mold.In some cases, shaped percursor parts can be machined from other moldedor extruded shapes.

In a typical operation, the ground molding composition is firstpreformed to eliminate trapped air and is electrically preheated to 230°F. (110° C.). This preform is then molded in a molding press using a5.5" diameter ram operated at 500 psi line pressure. The parts may becured at 300° F. (149° C.) for 4-5 minutes with a cavity pressure ofapproximately 1500 psi. Obviously, various other techniques may be used.

The precursor-shaped article is converted to a shaped vitreous carbonarticle by closely controlled thermal carbonization of the article in aninert atmosphere in a furnace until the maximum heat treatingtemperature is reached. Then the vitreous carbon article is cooled inthe closed furnace and in the inert atmosphere. Usually large numbers ofprecursor moldings are treated in a single heating operation whileretained in graphite containers in the furnace.

In most cases the optimum firing cycle of time versus temperature isdetermined experimentally for each different shape since the geometry,particularly the wall thicknesses, of the molded part has a directbearing on the rate. Also the time-temperature relationship is dependenton the degradation characteristics of the final cured resin. Thevariations in firing cycles will be even greater if the articles havedifferent wall dimensions.

A typical firing cycle generally has a continually increasingtemperature and usually has variable rates of increase in differentparts of the cycle. During the firing, a substantial volume shrinkage ofthe article occurs, which is usually in the range of 15 to 25% in thosemoldings which contain no carbonaceous or other filler. The amount ofshrinking depends on the resin, the molding technique and conditions,and the firing cycle. These shrinkages are reproducible and sufficientlypredictable to permit manufacturing tolerances of ±0.005 inch.

During the firing of such unfilled molded parts, about 30-35% by weightof the part is lost as volatile gas. When carbonaceous fillers are usedwith the resin mixture, the shrinkage and weight loss is reduced inproportion to the filler content. To flush out the large amount of gasgenerated during the vitreous carbon formation, a stream of inert purgegas such as nitrogen, helium or argon is used, or alternatively, areduced pressure of 10⁻² torr or less may be applied. The outgassing ispredominant in certain temperature ranges. For example, from roomtemperature up to 500°-700° F. (260°-371° C.), the temperature increaseis typically at a rate of 1°-5° F. per hour. Above 700° F. (371° C.),the temperature can be increased much more rapidly, as from 10° to 50°F. per hour. Generally for most parts, the temperature above 700° F.(371° C.) is increased at a rate of 10° F. per hour up to 800°-850° F.(427°-455° C.), and thereafter at 20°-50° F. per hour to the maximumtemperature which generally need not be above 1800° F. (982° C.). Insome cases the maximum temperature need not be above 1000° F. (538° C.).Where high thermal stability is required in the shaped vitreous carbonproduct, the heating may be continued up to at least 2000° F. (1093° C.)and in some cases, up to at least 3000° F. (1649° C.) and held at thattemperature for at least 24 hours. Then the temperature is droppedgradually at a rate of 10°-20° F. per hour.

Sometimes heating up to temperatures of about 300°-900° F. (149°-482°C.) is referred to as "carbonization" and heating to temperatures aboveabout 2100° F. (1149° C.) is sometimes referred to as "graphitization",heating in both cases being done gradually as illustrated above.

Where desired, the critical temperature regimes can be determined bythermogravimetric (TGA) and differential thermal analysis (DTA). Thethermal regimes thus determined are characteristics of the chemistry andthermal history of the molded phenolic resin part.

When the Novolac-resol co-reacted resin of this invention is to bemolded for purposes other than conversion to vitreous carbon, variousfillers other than the carbonaceous fillers recited above may be usedsuch as wood flour, asbestos, lime, calcium carbonate, MgO, glassfibers, etc., and any combination of these or other known modifiers maybe used in preparing molding compositions. The methods described abovemay be used for preparing blends or mixtures for molding purposes.

Accordingly it has been found that the co-reacted Novolac and resolresins prepared as described above may be used for preparing moldingcompositions for purposes other than the production of vitreouscompositions and that such molded products have various improvedproperties by virtue of the stress-free interaction of the Novolak andresol resins. In such cases the proportions of fillers and additivescorrespond substantially to those reported above for use in thecompositions to be converted to vitreous carbon.

In the addition of preformed Novolac to a solution of the resol prior toinitial or substantially complete dehydration of the resol, thepreformed Novolak may be completely dehydrated or partially dehydrated,advantageously at least 25 percent of the water initially present,preferably at least 50 percent of this water is removed prior toaddition to the resol. The product obtained after dehydration of themixture is completed is a grafted polymerization product.

The resin of this invention is prepared by adding preformed phenolicfurfuraldehyde Novolak, preferably phenol-furfuraldehyde Novolac, to anaqueous solution or suspension of a phenolic-aldehyde resol, preferablyphenol-formaldehyde resol, prior to the dehydration of the resol resin.The Novolac may be completely dehydrated or partially dehydrated at thetime of its addition to the resol. At the time of the addition, theresol may be partially dehydrated but the addition is preferably madebefore initiation of the dehydration.

As described above in the comments made regarding FIG. 1, the productobtained by this procedure is a graft polymerization product of improvedphysical properties. This is particularly true with regard to theproperties of the vitreous carbon produced therefrom. These new productsare a decided improvement over those produced according to othermethods. This improvement not only affects favorably the physicalproperties of the vitreous carbon plates, but practically eliminatesrejects of these plates on the basis of permeability. In the FIG. 1compositions the Novolak is PFUN produced by the procedure of Example Igiven below, and the resol is PFR produced by the procedure of ExampleIII, the graft polymerization product is produced according to ExampleV. In both cases, the proportions are 35 parts PFUN to 65 parts PFR andidentical amounts of filler and modifiers are used. It has also beenfound possible in accordance with the present invention to make thinvitreous carbon plates as large as 50"×50"×0.045".

The invention is illustrated by the following examples which areintended merely for purpose of illustration and are not to be regardedas limiting the scope of the invention or the manner in which it may bepracticed. Unless specifically indicated otherwise, parts andpercentages are given by weight.

EXAMPLE I Preparation of Phenol-Furfuraldehyde Novolac (PFUN)

Into a 4 liter resin vessel equipped with a mechanical stirrer,distillation condenser, heating mantel and thermometer is placed 2000gms (21.28 moles) of USP phenol and 1480 gms (15.25 moles) of furfural.This mixture is heated to 66° C. and 30.0 gms (0.36 mole) sodiumcarbonate added. The charge is then slowly heated to 121° C. at whichtemperature the heating mantel is removed. The reaction then becomesexothermic and the temperature continues to rise until boiling begins at135° C. The distillate is collected in a separating device and thefurfural layer is periodically drawn off and returned to the batchduring the course of the reaction. Distillation is continued for 3hours, 40 minutes with the batch temperature maintained between 133° and139° C. The resin is then discharged from the vessel and allowed to coolto a solid which has a melting point of 89° C. (192° F.), a yield of3230 gms, a glass transition temperature of 330° K. (134.6° F.). This isa non-curing Novolac resin, as shown when tested on a hot plate at 330°F., but when thoroughly mixed with 10 pph of hexa, has a set time at330° F. of 65-69 sec.

EXAMPLE II

The procedure of Example I is repeated except that midway in thedistillation, 30 gms of glycerylmonooleate is added, thoroughly mixedand the distillation continued. The resin has a melting point of 85.5°C. (186° F.), a glass transition temperature of 327° K. This is also anon-curing Novolac resin and with 10 pph of hexa, has a set time of67-68 sec.

EXAMPLE III Preparation of Phenol-Formaldehyde Resol Resin (PFR)

(a) Into equipment as used in Example I there is placed 1500 gms (15.96moles) of USP phenol, 1197 gms (20.75 moles) of aqueous formaldehyde(52%), 23 gms (0.16 mole) of hexa, and 7 gms (0.170 mole) of sodiumhydroxide (97%). This mixture is warmed to 90° C. and maitained at thistemperature for one hour. At the end of this period the reflux condenseris replaced with a vacuum distillation condenser and receiver. The batchis then maintained at a vacuum of 26" of Hg and heat supplied until thebatch temperature reaches 90° C. (194° F.). Then the vacuum is adjustedto 28" Hg and distillation continued for one hour. The reaction is thenterminated and the product discharged from the vessel. The amount ofdistillate water collected is 940 gms. The product weighs 1855 gms andhas a gradient bar melting point of 79.5° C. (175° F.), a glasstransition temperature as measured by differential scanning calorimetryof 321° K. (118.4° F.) and a hot plate set time of 17-18 seconds at 330°F. (165.5° C.).

(b) The above procedure is repeated using 36.3 gms of 30% aqueousammonia, (0.64 mole or 10.88 gms NH₃) but omitting the hexa. A specimenof the product indicates that the melting point is about 175° F. (79.5°C.) and is similarly grindable as the resol produced in (a).

(c) The procedure of Example III(a) is repeated except that 1058 gms(18.34 moles) of the aqueous formaldehyde solution is used. The productis a grindable resol.

(d) The procedure of Example III(a) is repeated using 1335 gms (23.15moles) instead of the 1197 gms of the aqueous formaldehyde. The productis a grindable resol.

EXAMPLE IV Preparation of Phenol-Formaldehyde Novolac Resin (PFN)

Into a 4 liter resin flask equipped with a mechanical stirrer, refluxcondenser and thermometer is placed 2000 gms (21.28 moles) USP phenol;882 gms (15.28 moles) aqueous formaldehyde (52%); 200 gms water and 12gms (0.10 mole) phosphoric acid (85%). The pH of the resulting mixtureis 1.05. This mixture is then heated to reflux and refluxed a total of 5hours. The free formaldehyde content of the mixture at this point isfound to be 0.84%. At this point, the reflux condenser is replaced witha distillation condenser and batch distilled under atmospheric pressurefor one hour until the batch temperature reaches 160° C. At this point amixture of 173 gms (3.0 moles) of 51% aqueous formaldehyde mixed with 70gms of water is slowly added to the mixture over a period of 36 minutes.During the addition, the batch temperature drops to 142° C. When all theaqueous formaldehyde has been added, the batch is held at 142°-150° C.for 15 minutes. Then the receiver on the distillation condenser isreplaced with a vacuum receiver to allow completion of the batch undervacuum. The resin is then dehydrated to a batch temperature of 165° C.under vacuum of 28 inches of mercury. The vacuum is released and theresin discharged from the vessel to yield 2027 gms of product, whichexhibits a gradient bar melting point of 223° F. and a glass transitiontemperature as measured by differential scanning calorimetry of 70° C.(158° F.). This resin is a non-curing Novolac as shown when tested on ahot plate at 330° F. However, when thoroughly bended with 10 parts perhundred (pph) of hexa, it has a set time of 24-25 sec. when heated at300° F. (166° C.).

EXAMPLE V Preparation of a Polyhydroxymethylphenol GraftedPhenol-Furfural Novolac-Ratio of Grafting Resol to Phenol-FurfuralNovolac=90/10

Into a 4 liter resin flask equipped with a 4-necked top bearing athermometer, reflux condenser, mechanical stirrer and stopper is placed1712 grams (18.21 moles) phenol, 1199 grams (20.78 moles) formaldehyde(52%). This mixture is cooled to 39° C. at which point 8.0 grams (0.2moles) sodium hydroxide and 85.6 grams (0.61 moles)hexamethylenetetramine are added. This mixture is heated to 90° C. overa period of 30 minutes and held at 90° C. for 30 minutes. The refluxcondenser is then replaced with a vacuum distillation apparatus and thebatch cooled rapidly by vacuum distillation at 26" of vacuum, to atemperature of 63° C. With a heating mantel variable resistor set at 56,250 grams of phenol-furfural Novolac (from Example I), which has beenfine ground to pass through a 60-mesh screen is added. The totaladdition time is 2 minutes. During the addition, the temperature isallowed to rise slowly to 64° C. When the addition is complete, thevessel is closed and vacuum distillation effected at 26" of mercuryvacuum to a temperature of 92° C. At this point a continuous readingwatt meter attached to the drive motor reads 110 watts at a speedsetting of 5. The resin is discharged to a pan to cool. Upon cooling,the resin is found to have a melting point of 84° C. by the gradient barmethod and a set time of 30.5 seconds at 165° C. by the stroke curemethod. The yield of graft copolymer is 2459 grams.

The product of the above reaction is then ground to pass through a60-mesh screen and placed on a differential two-roll compounding mill,the front roll of which is maintained at 121° C. and the back roll at27° C. This resin is then melted and compounded without additives for atotal of 17 minutes to give a product having a Brabender minimum torqueand duration of 2700 metergrams and 40.5 seconds, respectively. ThisBrabender measurement is performed on a standard Brabender plasticorderequipped with a half size head and roller blades. The temperature of themeasurement is 125° C. at 60 rpm with a connector setting of 1.5, asensitivity of 45(X5) with no suppression of torque.

The product is then molded in a standard transfer press using 600 psi ofline pressure to yield standard ASTM compressive strength, tensilestrength, flexural strength, Izod impact strength, and dielectricstrength specimens. These moldings are then tested with the followingresults:

Specific Gravity--1.28

Compressive Strength, psi--32,040

Flexural Strength, psi--14,366

Izod Impact Strength, ft-lb/in.--0.24 (notched)

Tensile Strength, psi--7,420

Dielectric Strength, v/mil--272

Deflection Temperature at 264 psi--367° F. (186° C.)

As illustrated in Example V, the Novolac is advantageously added afterrefluxing and preferably when sufficient removal of water has beenperformed under vacuum to effect a desired amount of cooling,advantageously 55°-70° F. If desired, the cooling may be effected byother means and the Novolac added after refluxing and before waterremoval is initiated. Water removal is effected, in either case, afterthe Novolac is added.

EXAMPLE VI Preparation of a Polhydroxymethylphenol GraftedPhenol-Furfural Novolac. Ratio of Grafting Resol to Phenol-FurfuralNovolac=80/20

The procedure of Example V is repeated using 1522 grams (16.19 moles) ofphenol, 1066 grams (18.48 moles) of formaldehyde (52% solution), 7.10grams (0.178 moles) of sodium hydroxide, 76.1 grams (0.54 mole) ofhexamethylenetetramine, and 250 grams of the phenol-furfural Novolac ofExample I. The addition time is 3 minutes and the temperature is allowedto rise slowly to 81° C. Vacuum distillation is effected at 24.8 inchesof mercury vacuum to a temperature of 93° C. The watt meter reading is120 watts at a speed setting of 5. The recovered resin has a meltingpoint of 183.8° C. and a set time of 30.5 seconds at 165° C. The yieldof graft copolymer is 2468 grams. Compounding is effected for 21 minutesto a Brabender minimum torque and duration of 2200 metergrams and 73.5seconds, respectively. The results from the tests of the moldings are:

Specific Gravity--1.28

Compressive Strength, psi--30,380

Flexural Strength, psi--12,544

Izod Impact Strength, ft.-lb./in.--0.24 (notched)

Tensile Strength, psi--6,700

Dielectric Strength, v/mil--275

Deflection Temperature at 264 psi--320° F. (160° C.)

EXAMPLE VII Preparation of a Polyhydroxymethylphenol GraftedPhenol-Furfural Novolac. Ratio of Grafting Resol to Phenol-FurfuralNovolac=70/30

The procedure of Example V is repeated using 1332 grams (14.17 moles) ofphenol, 932 grams (16.15 moles) of formaldehyde (52% solution), 6.20grams (0.156 moles) of sodium hydroxide, 66.6 grams (0.48 mole) ofhexamethylenetetramine, and 750 grams of the phenol-furfural Novolac ofExample I. The addition time is 12 minutes and the temperature isallowed to rise slowly to 68° C. Vacuum distillation is effected at 25inches of mercury vacuum to a temperature of 92° C. The watt meterreading is 120 watts at a speed setting of 5. The recovered resin has amelting point of 82° C. and a set time of 31.5 seconds at 165° C. Theyield of graft copolymer is 2480 grams. Compounding is effected for 20minutes to a Brabender minimum torque and duration of 2000 metergramsand 73.5 seconds, respectively. The results from the tests of themoldings are:

Specific Gravity--1.28

Compressive Strength, psi--29,420

Flexural Strength, psi--9,728

Izod Impact Strength, ft.-lb./in.--0.24 (notched)

Tensile Strength, psi--6,187

Dielectric Strength, v/mil--304

Deflection Temperature at 264 psi--297° F. (147° C.)

EXAMPLE VIII Preparation of a Polyhydroxymethylphenol GraftedPhenol-Furfural Novolac. Ratio of Grafting Resol to Phenol-FurfuralNovolac=60/40

The procedure of Example V is repeated using 1142 grams (12.15 moles) ofphenol, 799 grams (13.85 moles) of formaldehyde (52% solution), 5.33grams (0.133 moles) of sodium hydroxide, 57.1 grams (0.41 mole) ofhexamethylenetetramine, and 1000 grams of the phenol-furfural Novolac ofExample II. The addition time is 5 minutes and the temperature isallowed to rise slowly to 77° C. Vacuum distillation is effected at 24inches of mercury vacuum to a temperature of 93° C. The watt meterreading is 120 watts at a speed setting of 5. The recovered resin has amelting point of 86° C. and a set time of 28.5 seconds at 165° C. Theyield of graft copolymer is 2488 grams. Compounding is effected for 19.5minutes to a Brabender minimum torque and duration of 2200 metergramsand 45 seconds, respectively. The results from the tests of the moldingsare:

Specific Gravity--1.2

Compressive Strength, psi--26,780

Flexural Strength, psi--12,351

Izod Impact Strength, ft.-lb./in.--0.24 (notched)

Tensile Strength, psi--4,736

Dielectric Strength, v/mil--320

Deflection Temperature at 264 psi--261° F. (127° C.)

EXAMPLE IX Preparation of a Polhydroxymethylphenol GraftedPhenol-Furfural Novolac. Ratio of Grafting Resol to Phenol-FurfuralNovolac=50/50

The procedure of Example V is repeated using 1500 grams (15.96 moles) ofphenol, 1050 grams (18.2 moles) of formaldehyde (52% solution), 7 grams(0.175 moles) of sodium hydroxide, 75 grams (0.54 mole) ofhexamethylenetetramine, and 1933 grams of the phenol-furfural Novolac ofExample I. The addition time is 46 minutes and the temperature isallowed to rise slowly to 77° C. Vacuum distillation is effected at 19inches of mercury vacuum to a temperature of 89° C. The watt meterreading is 90 watts at a speed setting of 5. The recovered resin has amelting point of 84° C. and a set time of 34.5 seconds at 165° C. Theyield of graft copolymer is 3904 grams. Compounding is effected for 23minutes to a Brabender minimum torque and duration of 2400 metergramsand 120 seconds, respectively. The results from the tests of themoldings are:

Specific Gravity--1.28

Compressive Strength, psi--25,860

Flexural Strength, psi--10,944

Izod Impact Strength, ft.-lb./in.--0.26 (notched)

Tensile Strength, psi--7,640

Dielectric Strength, v/mil--280

Deflection Temperature at 264 psi--228° F. (108° C.)

EXAMPLE X Preparation of a Polhydroxymethylphenol Grated Phenol-FurfuralNovolac. Ratio of Grafting Resol to Phenol-Furfural Novolac=30/70

The procedure of Example V is repeated using 571 grams (6.08 moles) ofphenol, 399 grams (6.93 moles) of formaldehyde (52% solution), 2.66grams (0.066 moles) of sodium hydroxide, 28.54 grams (0.204 mole) ofhexamethylenetetramine, and 1750 grams of the phenol-furfural Novolac ofExample II. The addition time is 22 minutes and the temperature isallowed to drop slowly to 66° C. Vacuum distillation is effected at 24inches of mercury vacuum to a temperature of 90° C. The watt meterreading is 100 watts at a speed setting of 4.5 The recovered resin has amelting point of 87° C. and a set time of 41.5 seconds at 165° C. Theyield of graft copolymer is 2497 grams. Compounding is effected for 37minutes to a Brabender minimum torque and duration of 1900 metergramsand 105 seconds, respectively. The results from the tests of themoldings are:

Specific Gravity--1.28

Compressive Strength, psi--17,380

Flexural Strength, psi--6,528

Izod Impact Strength, ft.-lb./in.--0.25 (notched)

Tensile Strength, psi--3,093

Dielectric Strength, v/mil--285

Deflection Temperature at 264 psi--187° F. (86° C.)

EXAMPLE XI Preparation of a Polhydroxymethylphenol GraftedPhenol-Furfural Novolac. Ratio of Grafting Resol to Phenol-FurfuralNovolac=20/80

The procedure of Example V is repeated using 380.5 grams (4.05 moles) ofphenol, 266.4 grams (4.62 moles) of formaldehyde (52% solution), 1.78grams (0.045 moles) of sodium hydroxide, 19.03 grams (0.136 mole) ofhexamethylenetetramine, and 2000 grams of the phenol-furfural Novolac ofExample I. The addition time is 30 minutes and the temperature isallowed to drop slowly to 78° C. Vacuum distillation is effected at 19inches of mercury vacuum to a temperature of 80° C. The watt meterreading is 150 watts at a speed setting of 4. The recovered resin has amelting point of 110° C. and a set time of 33.5 seconds at 165° C. Theyield of graft copolymer is 2795 grams. Compounding is effected for 5.5minutes to a Brabender minimum torque and duration of 2500 metergramsand 52.5 seconds, respectively. The results from the tests of themoldings are:

Specific Gravity--1.28

Compressive Strength, psi--27,840

Flexural Strength, psi--9,024

Izod Impact Strength, ft.-lb./in.--0.24 (notched)

Tensile Strength, psi--4,580

Dielectric Strength, v/mil--253

Deflection Temperature at 264 psi--334° F. (168° C.)

EXAMPLE XII Demonstration of the Formation of a Graphite-FilledComposition

The resins from Examples I and IIIa are independently ground to passthrough a 0.05" screen and blended as follows:

Resin from Example I (PFUN)--850 grams

Resin from Example IIIa (PFR)--1500 grams

Powdered Graphite--2560 grams

Powdered Hexamethylenetetramine--100 grams

Stearyl Stearate--20 grams

Furfural--50 grams

Stearic Acid--50 grams

After blending for one hour in a ribbon blender, this mixture iscompounded on a two-roll differential mill with the front rollmaintained at 200° F. (93° C.) and the back roll at 300° F. (149° C.).The mill time is 15 seconds after complete melting of the resin. Thesheet is then stripped from the roll, cooled and ground to a particlesize of 6-80 mesh as measured on U.S. Standard Sieves. This powder ismeasured for plasticity and curing characteristics on the Brabenderplasticorder described in Example V and is found to have a minimumplasticity of 500 metergrams and a flow duration of 285 seconds at 125°C. This material is then molded by transfer molding to sheets22.5"×27.5"×0.045" thickness. Ordinary transfer molding is notreproducibly successful with this material because of insufficient flowduration. However, it can be molded successfully and reproducibly usingcompression molding techniques with 868 grams of 2" preforms weighing 62grams each, on a large 600 ton compression press. The cavity pressure inthis molding in 1500 psig and the plates are molded at 300° F. (149° C.)for 3-4 minutes. These plates are successfully converted to graphitefilled vitreous carbon of acceptable properties by the method describedbelow in Example XIV.

EXAMPLE XIII Demonstration of Resole Grafted Novolac Resin Blended withGraphite and Other Additives

The resin from Example VII is ground to pass through a 0.05" screen andblended with the following ingredients:

Resin from Example VII--2350 grams

Powdered Graphite--2560 grams

Powdered Hexamethylenetetramine--100 grams

Stearyl Stearate--20 grams

Furfural--50 grams

Stearic Acid--50 grams

After blending for one hour in a ribbon blender, this mixture iscompounded on a two-roll differential mill with the front rollmaintained at 200° F. (93° C.) and the back roll at 300° F. (149° C.).The mill time is 15 seconds after complete melting of the resin. Thesheet is then stripped from the roll, cooled and ground to a particlesize of 6-80 mesh as measured on U.S. Standard Sieves. This powder ismeasured for plasticity characteristics on the Brabender plasticorderdescribed in Example XIX and is found to have a minimum plasticity (lowtorque) of 400 metergrams and a flow duration of 435 seconds at 125° C.Conventional mixtures of single-stage and two-stage resins blended withidentical types and amounts of fillers in a identical formula andcompounded identically, give Brabender values of 500 metergrams and 285seconds flow duration. This demonstrates the desirable and unexpectedfeatures of these resins of increased flow duration and fluidity. Theseare features which allow this material to fill complex molds beforegelation occurs thereby allowing curing to take place under highpressure to give dense void free parts. Because of the demonstratedimprovements in flow behavior and physical homogeneity it is believedthat the grafted Novolac of this invention is superior to mixtures ofsimilar resins. This is molded according to the transfer molding methodinto sheets 22.5"×27.5"×0.045" thickness. Alternatively, the sheets canalso be molded into similar plates using compression molding techniqueswith 868 grams of 2" preforms weighing 62 grams each on a large 600 toncompression press. The cavity pressure in this molding is 1500 psig andthe plates are molded at 300° F. (149° C.) for 3-4 minutes. These platesare successfully converted to graphite filled vitreous carbon ofexcellent properties by the method described below in Example XIV.

EXAMPLE XIV Carbonization of the Moldings of Examples XII and XIII

To evaluate the carbonizability of these materials, the plates fromExamples XII and XIII are placed in a graphite container in a furnacehaving a nitrogen atmosphere. The carbonization cycle used is thatdescribed by Thornbury and Morgan (Soc. Plast. Eng. PACTEC 1975, Sept.16-18, 1975, p. 47). The temperature in the furnace is raised graduallyat a rate about 2°-3° F. per hour to a temperature of 700° F. (371° C.)at which point the temperature increase rate is adjusted to about 10° F.per hour up to 800°-850° F. (427°-454° C.) and, thereafter, at a rate ofabout 30° F. per hour to 1800° F. (982° C.) which temperature ismaintained for about 25 hours. Then while the nitrogen temperature ismaintained in the closed furnace, the temperature is decreased graduallyat a rate of about 10°-20° F. per hour to room temperature. Impermeableplates of vitreous carbon of excellent quality are obtained in eachcase.

EXAMPLE XV

The procedure of Example XIV is repeated a number of times with similarresults using respectively the coreacted resins of Examples VI, VIII andIX (which have PFR/PFUN ratios of 80/20; 60/40 and 50/50 respectively),each of which resins is mixed with graphite according to the procedureof Example XIII.

EXAMPLE XVI

The procedures of Examples I, V, XIII and XIV are repeated a number oftimes with satisfactory results in producing vitreous carbon using:

(a) An equivalent amount of meta-cresol in place of the phenol inpreparing the Novolac and the resol and these are used in the procedureof Example V;

(b) An equivalent amount of p,p'-diphenylolmethane is used in place ofphenol in preparing the Novolac used in the procedure of Example V;

(c) An equivalent amount of beta-naphthol is used in place of phenol inpreparing the resol used with the PFUN in the procedure of Example V.

In order to show the difference between the use of a phenol-formaldehydeNovolac and a phenol-furfuraldehyde Novolac as used in the practice ofthis invention, the following Example XVII describes experiments testingthe addition of a phenol-formaldehyde Novolac (PFN) to a series ofphenol-formaldehyde resols (PFR) prior to dehydration of the resol.These experiments are performed on a series of mixtures in which theweight ratio of resol to Novolac or PFR/PFN ranges from 40/60 to 80/20.The PFN is prepared by the procedure described in example IV. In thepreparations according to this invention, The dehydration is conductedunder vacuum until the wattage being applied to the agitator or stirrerreaches a value correlated to the approximate melting point desired inthe resin product. As shown in Example V, this requires a watt readingof 110 for an agitator motor speed setting of 5. Completion of reactionmay also be indicated by the amount of distillate water collected, thecalculation being based on the amount of water added in the formaldehydesolution plus that freed by reaction of the CH₂ O with the phenol. Thedistillate is primarily water with 2% by weight of free formaldehyde and5% by weight of free phenol. In the reactions reported below in ExampleXVII, neither of these measures indicated a completion of reaction priorto the gellation which occurred in each case. Moreover, resols preparedby standard procedures are not grindable and require the presence ofhexa or ammonia as shown in Example III a, b, c and d to give grindablecharacter to the resol. In a number of the runs of Example XVII where nohexa is used, the product is a rubbery gel. In an attempt to produce agrindable resin, hexa is used in Run C but this results in a muchquicker gellation than is produced in Runs A, B and D.

EXAMPLE XVII Attempted Preparation of PFR-PFN Grafted Resins

Four experiments are performed in a 4000 ml resin flask equipped with anagitator, thermometer and reflux condenser connected to a distillatecollector, plus a watt measuring device adapted to read the wattagesupplied to the agitator motor. In this flask there are placedappropriate amounts of USP phenol, formaldehyde (as a 52% aqueoussolution) and NaOH as a catalyst. In each case the mixture of phenol andaqueous formaldehyde is cooled to 40° C. and the NAOH is added. Thetemperature is then raised to 90° C. and held at this temperature forabout 1/2 hour. Then the equipment is adapted for vacuum distillationand the phenol-formaldehyde Novolak (PFN) is added in the form of a finepowder. A vacuum of about 26 inches of mercury is applied but completionof reaction is never reached as would be indicated by the wattagereading or by the amount of distillate water collected. The proportionsof reagents, conditions of reaction and results obtained are reportedbelow in Table A.

                  TABLE A                                                         ______________________________________                                        Run No.       A        B        C     D                                       ______________________________________                                        Phenol (gms)  761      1142     1500  1522                                    Phenol (moles)                                                                              8.10     12.15    15.96 16.19                                   Formaldehyde (52%):                                                                         533      799      1381  1066                                    Aqueous solution (gms)                                                        CH.sub.2 O (gms)                                                                            277.16   415.48   718.64                                                                              554.32                                  CH.sub.2 O (moles)                                                                          17.77    13.85    23.94 18.48                                   Phenol/CH.sub.2 O                                                                           1/2.19   1/1.14   1/1.50                                                                              1/1.14                                  (mol. ratio)                                                                  NaOH (gms)    3.55     5.33     7     7.1                                     Hexa (gms)    --       --       105   --                                      PFN (gms)     1500     1000     1333  500                                     Ratio (Resol/Novolak)                                                                       40/60    60/40    70/30 80/20                                   Vacuum (inches Hg.)                                                                         26-28    26-28    26    26                                      Temp. (°C.)                                                                          9-95° C.                                                                        90-95° C.                                                                       90° C.                                                                       90-94° C.                        Result        Gelled   Rubbery  Gelled                                                                              Rubbery                                                        Gel            Gel                                     *Time before gellation                                                                      6 hrs.   5 hrs.   13 min.                                                                             6 hrs.                                                15"      56"            23"                                     Watts at motor speed                                                                        50       70**     --    --                                      setting of 5                                                                  Distillate collected                                                                        380      --       --    726                                     (gms)                                                                         Percent of theoretical                                                                      58.7%    --       --    49%                                     water                                                                         ______________________________________                                         *After the addition of PFN is completed and vacuum is applied.                **With motor speed setting of 7.                                         

The process of this invention is much simpler and gives betterreproducibility than obtained with mixtures of resins as described inapplication Ser. No. 50,531.

Where reference is made to phenol-furfural Novolacs, it is intended thatthis includes Novolaks in which other aldehydes may be used to replace aminor amount of furfuraldehyde in the formation of the resin. Thus inreferring to a phenol-furfural Novolac, it is intended to includeNovolacs in which the major molar amount of the aldehyde used tocondense with the phenol is furfural. In other words, while 100 molarpercent of furfural is preferred for this purpose, it is found that solong as at least 50 molar percent of the condensing aldehyde isfurfural, the resulting Novolac gives satisfactory results for thepurpose of this invention.

Where there is poor plasticity during molding, it is generally necessaryto use higher pressures. As indicated in the above examples, pressuresof 1500 psi are used satisfactorily with PFUN-coreacted-PFR-graphitemixtures and, in most cases, the molding plasticity may be sufficientlyimproved to permit lower pressures, preferably 800-1500 psi. Pressuresabove 1500 psi and more particularly above 2000 psi may cause stressesand strains in the molded products and in the vitreous carbon producedtherefrom. These stresses and strains very often cause cracks andparticularly microcracks in the products. These stresses and theaccompanying cracks and microcracks are avoided or at least reduced bythe lower molding pressures allowed by the improved molding plasticityof the coreacted PFUN-PFR combinations of this invention.

As pointed out above, the co-reacted product of thephenol-furfuraldehyde Novolac with the resol has a molding plasticitywhich allows the viscous mass to flow uniformly and readily tocompletely fill the mold. This is particularly evident when the resin isfilled with a substantial amount of filler such as graphite. Thisimproved plasticity has made it possible to mold and convert to vitreouscarbon PFUN-coreacted-PFR-graphite filled plates as large as 50"×50" andhaving a thickness of 0.04-0.05 inch and having excellent resistance topermeability and freedom from cracks and pits. PFN-PFR-graphite filledmixtures do not have satisfactory plasticity and flow for this purpose.The preferred ratios of PFUN/PFR run from 20/80 to 50/50.

The vitreous carbon made from the co-reacted products described aboveare very much improved in freedom from pits and holes. This improvementwith respect to freedom from pits and holes and cracks in the vitreouscarbon products of this invention is evidenced by improved resistance topermeability and also in the reduction in the number of rejects when thevitreous carbon products, such as large thin plate, are subjected tovarious tests to determine whether they will meet the conditions inwhich they will be exposed for use in fuel cells.

In parent applications the examiner has cited Rice et al U.S. Pat. No.3,998,906 and Japanese Patent No. 53-75294. Both of these patents aredirected to the preparation of resins used for binding and particles formaking molds for metal casting. Neither of these references teaches theunexpected superiority of a phenol-furfural Novolac resin in suchmixtures as taught herein, nor does either reference teach the advantageof adding an amine, such as hexamethylenetetramine to the resol prior tothe addition of the Novolac.

The following examples demonstrate the inferiority ofphenol-formaldehyde Novolacs (PFN) mixtures compared to thephenol-furfural Novolacs (PFUN) mixtures shown in Examples I, II andVI-XIV for the purposes of this invention. These examples alsoillustrate the importance of adding hexa to the resol-Novolac reactionmixture to prevent gelation and to give improved molding plasticity. Forcomparative purposes in these examples, the ratio of phenol formaldehyderesole (PFR) to PFN or PFUN is 60/40 since this has been found to be apreferred ratio.

Each of the resins produced in these examples is mixed with graphiteaccording to the procedure of Example XII and molded at 300° F. for 3-4minutes (using 3-5 specimens of each resin) into plates havingdimensions of 22.5 inches×27.5 inches ×0.045 inch using a 600 ton pressoperating at 2000 psi line pressure. The various plates are inspectedcarefully for defects and flaws and graded by the followingdesignations: blisters (B); knitlines (KL); hole in center (HC);porosity (P); short corner (SC); slight short corner (SSC); short side(SS) and no visible flaws (NF).

Examples XVII through XXIII demonstrate the use of PFR/PFN combinationsin which only a limited amount of hexa is added prior to the graftingoperation, the amount being approximately the small amount required onlyfor the resol improvement, with varying amounts of water removed fromthe Novolac prior to its addition to the resol components. Examples XXIVand XXV demonstrate the use of PFR/PFN combinations in which largeramounts of hexa are added prior to or during the grafting operation withvarying amounts of water removed from the Novolac prior to its additionto the resol components. Reference in these examples to "without hexa"means the addition of no more than the limited small amount of hexa forthe resol and "with hexa" means the addition of sufficient hexa to actin the grafting operation.

As will be noted, the procedures of these examples do not producesatisfactory plates.

EXAMPLE XVII

This example follows the procedure of Example 3 of Japanese Pat. No.53-75294. A resol precondensate is prepared by placing in a reactorequipped with a reflux condenser: 940 gms (10 moles) of phenol; 1214 gmsof 42% formalin (aqueous solution of formaldehyde) (17 moles); and 47gms of trisodium phosphate. The mixture is refluxed 1.5 hours. Theresulting 2196 gms of precondensate has a resin content of 50% andvolatile portion of 50%.

In a separate, similar reactor are placed 940 gms of phenol, 571 gms of42% formalin and 9.4 gms oxalic acid and this mixture refluxed for 2hours to give 1518 gms of Novolac resin precondensate.

The entire amount (2196 gms) of the resol precondensate are added to 844gms of the Novolac precondensate and the resulting mixture is gentlyreacted under reduced pressure and removing water and unreacted phenoluntil the temperature reaches 90° C., at which time the reaction mixturegelled and was removed from the reactor and cooled to yield 2896 gms ofsemi solid gel. The reaction is repeated twice with each batch gellingsimilarly.

This resin is molded into a plate as described above. The plate iscompletely unsatisfactory for further processing into vitreous carbonsince it has short corners, short sides, knitlines and holes in thecenter.

EXAMPLE XVIII

The procedure of Example 4 of Japanese Pat. No. 53-75294 is followed.The procedure of Example XVII is repeated and to the 1518 gms of Novolacresin produced there is added 725 gms of the resol resin produced. Themixture is further processed as in Example XVII to yield 1452 gms ofsolid resin, which by gradient bar melt point melts at 180° F. andexhibits a somewhat rubbery set at 330° F. in 30 sec.

When this resin is molded into a plate as described above, the sameunsatisfactory results are obtained as in Example XVII.

EXAMPLE XIX

The procedure of Example 1 of Rice U.S. Pat. No. 3,998,906 is followed.Prepolymer A (a Novolac) is prepared by mixing in a reactor equippedwith temperature control means and refluxing facilities 1177 parts ofUSP phenol, 395 parts of 95% paraformaldehyde (5% water), 1759 parts ofwater to equate the paraformaldehyde to aqueous formaldehyde and 200parts of 50% aqueous NaOH solution. The first three ingredients aremixed and a small initial amount of the NaOH solution is added todissolve the paraformaldehyde. The temperature is raised to 50°-55° C.and the remainder of the NaOH solution is added. Then the temperature israised to 90° C. and the mixture reacted for 30 minutes, after which thetemperature is lowered to 80°-85° C. and reaction continued for 60minutes. The product is then cooled to room temperature.

Prepolymer B (Resol) is prepared in a similar reactor using 1177 partsof USP phenol, 925 parts of 95% paraformaldehyde, 2177 water and 180 gmsof 50% aqueous NaOH solution. The procedure of the preceding paragraphis followed except that the first heating is to 60°-65° C. and afteraddition of the balance of the NaOH solution, the temperature is loweredto 50°-55° C. and reaction continued for 120 minutes. Then reaction iscontinued at 45°-50° C. for an additional 60 minutes before the reactionproduct is cooled to room temperature.

Prepolymer A (938 parts) and prepolymer B (938 parts) are added to asimilar reactor together with 33.8 parts of 50% NaOH solution and thetemperature raised to 85°-87° C. for a sufficient period that thereaction mixture reaches a viscosity of 600-700 centipoises (measured at25° C.). Then the reaction temperature is lowered to 75°-80° C., 90.2parts of 50% aqueous NaOH solution is added and reacted at 75°-80° C.until the resultant resin reaches a viscosity of 400-500 cps (measuredat 25° C.) at which time the resin is cooled to room temperature.

Three plates are molded from this resin using the procedure describedabove. None of these plates are satisfactory, with all three havingshort corners and porosity and two also having short sides, and eitherknitlines or holes.

EXAMPLE XX 60/40 PFR/PFN Without Hexa During Grafting (25% Water RemovedFrom PFN)

(a) Into equipment as used in Example I there is placed 2000 gms (21.28moles) of USP phenol, 822 gms (15.28 moles) of aqueous formaldehyde(52%), 200 gms water and 2 gms (0.10 mole) of phosphoric acid (85%).This mixture is then heated to reflux and refluxed for a total of 5hours. At this point the reflux condenser is replaced with adistillation condenser and batch distilled until the batch temperaturereaches 160° C. Then a mixture of 173 gms (3.0) moles of 51% aqueousformaldehyde mixed with 70 gms of water is slowly added to the mixtureover a period of 36 minutes. During the addition the batch temperaturedrops to 142° C. When all the aqueous formaldehyde has been added, thebatch is held at 142°-150° C. for 15 minutes. Then the receiver on thedistillation condenser is replaced with a vacuum receiver to allowcontinuation of water removal. Then the vacuum is adjusted to 28" Hg anddistillation continued until 25% of the water is collected (based on theamount of water collected with 100% removal). This PFN product isretained for subsequent use below.

(b) Into a 4-liter resin flask equipped with a 4-necked top bearing athermometer, reflux condenser, mechanical stirrer and stopper is placed1142 grams (12.15 moles) USP phenol and 799 grams (13.85 moles) aqueousformaldehyde (52%). This is cooled to 39° C. and there are added 51.7gms of hexa and 5.33 gms (0.133 moles) of sodium hydroxide. This mixtureis heated to 90° C. over a period of 30 minutes and held at 90° C. for30 minutes. The reflux condenser is then replaced with a vacuumdistillation apparatus and the batch cooled rapidly by vacuumdistillation at 26" of vacuum, to a temperature of 63° C. With a heatingmantel variable resistor set at 56, 2180 gms of the phenol formaldehydeNovolac (PFN) of (a) is added. During the addition, the temperature isallowed to rise slowly to 64° C. When the addition is complete, thevessel is closed and vacuum distillation is effected at 26" of mercuryvacuum to a temperature of 92° C. At this point a continuous readingwatt meter attached to the drive motor reads 110 watts at a speedsetting of 5. The resin is discharged to a pan to cool.

Three specimens are molded into plates as described above. All threeplates are defective with each of the three having holes and porosity,two having short sides and one of these two also having short corners.

EXAMPLE XXI 60/40 PFR/PFN Without Hexa During Grafting (50% WaterRemoved From PFN)

The procedure of Example XX is repeated except that 470 gms (50%) of thewater is removed from the Novolac (PFN) prior to its addition to theresol in (b). The resultant resin is likewise molded into five plates,four of which proved to be unsatisfactory, three of them having porosityand the fourth having holes and short corners, two of the three alsohaving short sides and one having short corners.

EXAMPLE XXII 60/40 PFR/PFN Without Hexa During Grafting (75% WaterRemoved From PFN)

The procedure of Example XX is repeated except that 705 gms (75%) of thewater is removed from the Novolac (PFN) prior to its addition to theresol in (b). The resultant resin is likewise molded into a plate whichbecause of short corners and short sides is unsatisfactory.

EXAMPLE XXIII 60/40 PFR/PFN Without Hexa During Grafting (100% WaterRemoved From PFN)

The procedure of Example XX is repeated except that 940 gms (100%) ofthe water is removed from the Novolac (PFN) prior to its addition to theresol in (b). The resultant resin is grindable but when used in themolding of two plates as described above, the two plates are completelyunsatisfactory because of holes in center, short corners, short sidesand porosity.

EXAMPLE XXIV

60/40 PFR/PFN With Hexa During Grafting (25% Water Removed From PFN)

(a) Into equipment as used in Example I there is placed 1500 gms of USPphenol, 166 gms of water, 100 gms of hexa, 1800 gms of water and 364 gmsof paraformaldehyde (95%). A small amount of the caustic solution isadded and the heat turned on. The remainder of the caustic solution isadded slowly and the mixture is heated to 90° C. and held at thistemperature for 30 minutes. At this point the mixture is cooled to 85°C. and held here for 60 minutes. Then atmospheric distillation iseffected until 264 gms of water is collected, (25% of the amount that iscollected when all the water is removed) at which time the product(45.5% solids) is cooled and used as directed below in (b).

(b) Into a 4-liter resin flask equipped with a 4-necked top bearing athermometer, reflux condenser, mechanical stirrer and stopper is placed1142 grams (12.15 moles) USP phenol and 799 grams (13.85 moles) aqueousformaldehyde (52%). This is cooled to 39° C. and there are added 51.7gms of hexa and 5.33 gms (0.133 moles) of flake sodium hydroxide. Thismixture is heated to 90° C. over a period of 30 minutes and held at 90°C. for 30 minutes. The reflux condenser is then replaced with a vacuumdistillation apparatus and the batch cooled rapidly by vacuumdistillation at 26" of vacuum, to a temperature of 63° C. To thismixture there is added 2045 gms of the phenol formaldehyde Novolac (PFN)from (a). When the addition is complete, the vessel is closed and vacuumdistillation is effected at 24" of mercury vacuum to a temperature of70° C. At this point a continuous reading watt meter attached to thedrive motor reads 120 watts at a speed setting of 5. The resin isdischarged to a pan to cool.

The resultant grafted resin is compounded and molded according to theprocedure described above into four plates, none of which issatisfactory. All four have pores and in addition two have knitlines,hole in center and slight short corners.

EXAMPLE XXV 60/40 PFR/PRN With Hexa During Grafting (50% Water RemovedFrom PFN)

The procedure of XXIV is repeated except that 50% of the water isremoved from the Novolac (a) before it is added to the resol componentsin (b). The resultant grafted resin is compounded and molded accordingto the procedure described above into three plates, none of which issatisfactory. All three plates have short corners and pores and one alsohas short sides.

The following Examples XXVI through XXIX demonstrate the use of PFR/PFUNin which only enough hexa is added to affect the resol and none for thegrafting operation, with varying amounts of water removed from theNovolac prior to its addition to the resol components. None of theprocedures of these examples produce satisfactory plates.

EXAMPLE XXVI 60/40 PFR/PFUN Without Hexa During Grafting (25% WaterRemoved From PFUN)

(a) Into a 4 liter resin vessel equipped with a mechanical stirrer,distillation condenser, heating mantel and thermometer is placed 2000gms (21.28 moles) of USP phenol and 1480 gms (15.25 moles) of furfural.This mixture is heated to 65° C. and 30.0 gms (0.36 mole) sodiumcarbonate added. The charge is then slowly heated to 121° C. at whichtemperature the heating mantel is removed. The reaction then becomesexothermic and the temperature continues to rise until boiling begins at135° C. The distillate is collected in a separating device with furfuralreturned to the reaction mixture until 64.7 gms of water (25% of thewater) is collected. Temperature is decreased and 20 gms of emery oil isadded and stirred for 5 minutes. The resultant resin is discharged fromthe vessel and saved for use in (b).

(b) Into a 4 liter resin flask equipped with a 4-necked top bearing athermometer, reflux condenser, mechanical stirrer and stopper is placed1142 gms (12.15 moles) phenol, 799 grams (13.85) formaldehyde (52%).This mixture is heated to 90° C. over a period of 30 minutes and held at90° C. for 30 minutes. The reflux condenser is then replaced with avacuum distillation apparatus and the batch cooled rapidly by vacuumdistillation at 26" of mercury to a temperature of 63° C. With a heatingmantel variable resistor set at 56, 1667 gms of the phenol-furfuralNovolac (PFUN) from (a) is added. During the addition, the temperatureis allowed to rise slowly to 64° C. When the addition is complete, thevessel is closed and vacuum distillation is effected at 26" of mercuryvacuum to a temperature of 92° C. At this point a continuous readingwatt meter attached to the drive motor reads 110 watts at a speedsetting of 5. The resin is discharged to a pan to cool.

The resultant resin is molded into five plates as described above. Allfive plates are defective with each of the five having short corners,short sides and knitlines.

EXAMPLE XXVII 60/40 PFR/PFUN Without Hexa During Grafting (50% WaterRemoved From PFUN)

The procedure of Example XXVI is repeated except that 50% of the wateris removed from the Novolac (PFUN) prior to its addition to the resol in(b). The resultant resin is likewise molded into five plates asdescribed above, each of which proves to be unsatisfactory, all four ofthem having short corners, short sides and knitlines, with three of themalso having blisters.

EXAMPLE XXVIII 60/40 PFR/PFUN Without Hexa During Grafting (75% WaterRemoved From PFUN)

The procedure of Example XXVI is repeated except that 75% of the wateris removed from the Novolac (PFUN) prior to its addition to the resol in(b). The resultant resin is likewise molded into four plates asdescribed above. All four plates are unsatisfactory, each having shortcorners, short sides and knitlines, with three also having blisters andone of these three also having pores.

EXAMPLE XXIX 60/40 PFR/PFUN Without Hexa During Grafting (100% WaterRemoved From PFUN)

The procedure of Example XXVI is repeated except that all (100%) of thewater is removed from the Novolac (PFUN) prior to its addition to theresol in (b). The resultant resin is likewise molded into four plates asdescribed above. All four plates are unsatisfactory, each having shortcorners and knitlines, with three also having blisters.

The following Examples XXX through XXXIII demonstrate the use ofPFR/PFUN in which additional hexa is used for the grafting operation andare designated as "With Hexa". Varying amounts of water is removed fromthe Novolac (PFUN) prior to its addition to the resol components. Plateproduction from these resins are much more satisfactory.

EXAMPLE XXX 60/40 PFR/PFUN With Hexa During Grafting (25% Water RemovedFrom PFUN)

(a) A phenol-furfuraldehyde Novolac (PFUN) is prepared according to theprocedure of Example XXVI(a) in which in the water removal step only 25%of the water is removed.

(b) Into a 4 liter resin flask equipped with a 4-necked top bearing athermometer, reflux condenser, mechanical stirrer and stopper is placed1142 gms (12.15 moles) phenol and 799 grams (13.85 moles) formaldehyde(52%). The mixture is cooled to 39° C. and 5.33 gms of flake NaOH isadded. This mixture is heated to 90° C. over a period of 30 minutes andheld at 90° C. for 30 minutes. The reflux condenser is then replacedwith a vacuum distillation apparatus and the batch cooled rapidly byvacuum distillation at 26" of mercury to a temperature of 63° C. With aheating mantel variable resistor set at 56, 1667 gms of thephenol-furfural Novolac (PFUN) from (a) is added. During the addition,the temperature is allowed to rise slowly to 64° C. When the addition iscomplete, the vessel is closed and vacuum distillation is effected at26" of mercury vacuum to a temperature of 90° C. At this point acontinuous reading watt meter attached to the drive motor reads 120watts at a speed setting of 5. The resin is discharged to a pan to cool.

The resultant resin is molded into five plates as described above. Twoplates have no flaws, one has no flaws except for a very slight bubbleand two have short corners.

EXAMPLE XXXI 60/40 PFR/PFUN With Hexa During Grafting (50% Water RemovedFrom Novolac)

(a) A phenol-furfuraldehyde Novolac (PFUN) is prepared according to theprocedure of Example XXVI(a) except that in the water removal step 50%of the water is removed.

(b) In a separate reactor the procedure of Example XXX(b) is repeatedusing the Novolac of Example XXXI(a) in place of the Novolac used inExample XXX. Three plates are molded from this resin according to theabove-described procedure. All three plates are free of flaws.

EXAMPLE XXXII 60/40 PFR/PFUN With Hexa During Grafting (75% WaterRemoved From Novolac)

(a) A phenol-furfuraldehyde Novolac (PFUN) is prepared according to theprocedure of Example XXVI(a) except that in the water removal step 75%of the water is removed.

(b) In a separate reactor the procedure of Example XXX(b) is repeatedusing the Novolac of Example XXXII(a) in place of the Novolac used inExample XXX(b). Three plates are molded from this resin according to theabove-described procedure. Two of the plates have no flaws and the thirdhas a very slight short corner.

EXAMPLE XXXIII 60/40 PFR/PFUN With Hexa During Grafting (100% WaterRemoved From Novolac)

A grafted PFR/PFUN copolymer is prepared in accordance with theprocedure of Example VIII with substantially complete water removal fromthe Novolac. Eight plates are molded from this resin. All eight platesare free of flaws.

The results from the moldings of plates from Examples XVII throughXXXIII are summarized below in Table B. As indicated in the respectiveexamples the resol/Novolac ratio is 60/40 in each case. In each case theresol is phenol-formaldehyde resol (PFR). The abbreviations are asdefined above.

                                      TABLE B                                     __________________________________________________________________________               % Water                                                            Resin from Removed From                                                                          Hexa Plate                                                 Ex.   Novolac                                                                            Novolac Added?                                                                             No.                                                                              Flaws                                              __________________________________________________________________________    XVII* PFN  None    No   10A                                                                              SC,SS,KL,H                                         XVIII**                                                                             PFN  None    No   10B                                                                              SC,SS,KL,H                                         XIX***                                                                              PFN  None    No   54 SC,SS,P,KL                                         "     "    "       "    55 SC,SS,P,H                                          "     "    "       "    56 SC,P                                               XX    PFN  25      No    5 SS,H,P                                             "     "    "       "     6 SC,SS,HP                                           "     "    "       "     7 H,P                                                XXI   PFN  50      No   11 P                                                  "     "    "       "    12 None                                               "     "    "       "    13 SS,P                                               "     "    "       "    14 H,SC,SS,P                                          "     "    "       "    15 H,SC                                               XXII  PFN  75      No   16A                                                                              SC,SS                                              XXIII PFN  100     No   52 SC,SS,HC,P                                                                    (Does not form plate)                              "     "    "       "    53 SC,SS,HC,P                                                                    (Does not form plate)                              XXIV  PFN  25      Yes   1 K,P,H,SSC                                          XXIV  PFN  25      Yes   2 P                                                  "     "    "       "     3 P                                                  "     "    "       "     4 P                                                  XXV   PFN  50      Yes   8 SC,P                                               "     "    "       "     9 SC,P                                               "     "    "       "    10 SC,P,SS                                            XXVI  PFUN 25      No   21 SC,SS,KL                                           "     "    "       "    22 SC,SS,KL                                           "     "    "       "    23 SC,SS,KL                                           "     "    "       "    24 SC,SS,KL                                           "     "    "       "    25 SC,SS,KL                                           XXVII PFUN 50      No   29 SC,SS,KL,B                                         "     "    "       "    30 SC,SS,KL                                           "     "    "       "    31 SC,SS,KL,B                                         "     "    "       "    32 SC,SS,KL,B                                         XVIII PFUN 75      No   36 SC,SS,KL                                           "     "    "       "    37 SC,SS,KL,B                                         "     "    "       "    38 SC,SS,KL,B,P                                       "     "    "       "    39 SC,SS,KL,B                                         XXIX  PFUN 100     No   44 SC,KL,B                                            "     "    "       "    45 SC,KL                                              "     "    "       "    46 SC,KL,B                                            "     "    "       "    47 SC,KL,B                                            XXX   PFUN 25      Yes  16 None                                               "     "    "       "    17 SC                                                 "     "    "       "    18 None except for                                                               slight bubble                                      "     "    "       "    19 None                                               "     "    "       "    20 SC                                                 XXXI  PFUN 50      Yes  26 None                                               "     "    "       "    27 None                                               "     "    "       "    28 None                                               XXXII PFUN 75      Yes  33 SSC                                                "     "    "       "    34 None                                               "     "    "       "    35 None                                               XXXIII                                                                              PFUN 100     Yes  40 None                                               "     "    "       "    41 None                                               "     "    "       "    42 None                                               "     "    "       "    43 None                                               "     "    "       "    48 None                                               "     "    "       "    49 None                                               "     "    "       "    50 None                                               "     "    "       "    51 None                                               __________________________________________________________________________     *Jap. Pat. Ex. 3                                                              **Jap. Pat. Ex. 4                                                             ***Rice Pat. Ex. 1                                                       

As will be observed from examination of the results reported in theabove TABLE B, none of the PFR/PFN combinations, with or without theaddition of hexa, produced a grafted copolymer that is capable of beingmolded into plates as described in which the plates are without flaws(except for plate No. 12), or in other words satisfactory for subsequentcarbonizing to vitreous carbon plates. In summary only one of the 23plates formed is satisfactory.

Likewise, when the resin combination is PFR/PFUN and hexa is omitted, ofthe 17 plates formed, none is free of flaws or in other words none issatisfactory for subsequent carbonizing to vitreous carbon plates.

When hexa is added to the PFR/PFUN grafting operation, of the 19 platesformed, only three are unsatisfactory as having one flaw, one isborderline and the 15 others are free of flaws and satisfactory forcarbonizing to vitreous carbon plates.

In other words, 95.8% of the PFR/PFN plates, with or without hexa, areunsatisfactory and have flaws which make them unsatisfactory forsubsequent carbonization to vitreous carbon plates. Likewise, when thehexa is omitted in the grafting of PFR/PFUN resins, 100% or 17 out ofthe 17 plates prepared have flaws that make them unsatisfactory forsubsequent carbonization to vitreous carbon plates.

In contrast, the PFR/PFUN combinations of this invention in which atleast 25% of the water is removed from the Novolac and sufficient hexais added for the grafting operation, show that of the 19 plates moldedonly 3 or possibly 4, that is 15.8% or 21%, have flaws, with 84.2% or79% free of flaws. In a more preferred range of having 50%-75% of thewater removed from the Novolac before use in the grafting operation, outof 6 plates there is only one plate that has a defect, or in otherwords, 17%, with 83% of the plates without flaws and satisfactory forcarbonization to vitreous carbon. Also as stated above, whensubstantially 100% of the water is removed from the PFUN Novolac priorto addition, the plates are 100% flawless and suitable for subsequentcarbonization to vitreous carbon plates.

From the above it is concluded that the grafted combination offormaldehyde phenol resol with formaldehyde-furfuraldehyde in which atleast 25% advantageously at least 35%, preferably at least 50% or 75% ofthe water present during the Novolac preparation is removed prior toaddition to the mixture of resol components or during the early stage ofresol formation. Ideally substantially all of the water is removed fromthe Novolac before such addition.

As discussed above the hexa may be replaced by amines. Such aminesshould have one or more nitrogen atoms with at least one hydrogenattached to a nitrogen therein. In the reaction described herein itappears that there may be only one reaction per nitrogen atom havinghydrogen attached thereto. In the case of hexa there are four nitrogenscapable of reaction even though these do not have hydrogen attachedthereto. The equivalent weight of hexa is therefore the molecular weightdivided by 4, or 140/4 or 35. With the other amines the equivalentweight in each case is the molecular weight of an amine divided by thenumber of nitrogen atoms that have at least one hydrogen attached. Forexample ethyl amine has an equivalent weight of 45/1 or 45. Ethylenediamine has an equivalent weight of 60/2 or 30.

EXAMPLE XXXIV

The procedures of Examples I, VIII, XIII and XIV are repeated a numberof times using in place of the 57.1 grams (0.41 mole) ofhexamethylenetetramine of Example VIII the following equivalent amountsrespectively of the following amins:

(a) 73.4 gms of ethylamine

(b) 73.4 gms of dimethyl amine

(c) 152.5 gms of aniline

(d) 49.2 gms of ethylene diamine

(e) 88.6 gms of phenylene diamine

(f) 111.5 gms of N,N'-dimethyl-phenylene diamine

(g) 175.4 gms of N-methyl aniline

(h) 72.2 gms of N,N'-dimethyl-ethylene diamine

(i) 65.6 gms of propylene-diamine

(j) 139.4 gms of piperidine

(k) 77.1 gms of piperazine

In each case a grafted copolymer is produced in the repetitions ofExample VIII, plates are molded without flaws in the repetitions ofExample XIII and these are satisfactorily carbonized to vitreous carbonplates by the procedure of Example XIV.

While certain features of this invention have been described in detailwith respect to various embodiments thereof, it will of course beapparent that other modifications can be made within the spirit andscope of this invention, and it is not intended to limit the inventionto the exact details shown above except insofar as they are defined inthe following claims.

The invention claimed is:
 1. A process for preparing a vitreous carbonof improved freedom from pits and holes and much less subject tocracking and failure during formation and use, comprising the stepsof:(1) molding a moldable composition of improved mold flow propertiesprepared by the addition of a phenolic-aldehyde Novolac resin in whichat least 50 molar percent of said aldehyde is furfuraldehyde to anaqueous solution or suspension of a phenolic-aldehyde resol resin priorto the removal of 90 percent of the removable water from said resolresin solution or suspension, the proportions of said resins comprising20-80 parts by weight of said Novolac resin and 20-80 parts by weight ofsaid resol resin with the combined weight of said two resins comprising100 parts by weight, thereafter effecting coreaction of said resinstogether with an amine selected from the group consisting ofhexamethylenetetramine and amines in which there is at least onehydrogen connected to a nitrogen atom, the amount of said amine beingequivalent to 1-15 percent by weight of hexamethylenetetramine based onthe total weight of phenolic component, and removal of water from theresulting reaction mass while maintaining the resin in a moldablecondition, the Novolac resin having been prepared with the removal of atleast 25 percent by weight of the water removable during the Novolacpreparation, and prior to said molding intimately mixing said coreactedresins with 5-76 percent by weight of a finely divided carbonaceousfiller based on total molding composition, said molding being effectedat a temperature of 100°-180° C. and a pressure between 500 pounds persquare inch and 8 tons per square inch; and (2) heating the resultantmolded product gradually up to a final temperature of at least 1800° andholding at said final temperature for at least 24 hours.
 2. The processof claim 1 in which said amine is hexamethylenetetramine and thecarbonaceous filler is 35-65 percent by weight of the total moldablecomposition.
 3. The process of claim 1 in which the amount of said amineis equivalent to 2-8 parts by weight of hexamethylenetetramine per 100parts by weight of said Novolac resin.
 4. The process of claim 3 inwhich said amine is hexamethylenetetramine.
 5. The process of claim 2 inwhich the phenolic component in the Novolac is phenol.
 6. The process ofclaim 5 in which the phenolic component in the resol is phenol and thealdehyde in the resol is formaldehyde.
 7. The process of claim 6 inwhich the furfuraldehyde content in said Novolac is at least 75 molarpercent of the aldehyde component.
 8. The process of claim 6 in whichthe furfuraldehyde in said Novolac is approximately 100 molar percent ofthe aldehyde component.
 9. The process of any one of claims 1, 2, 3, 4,5, 6, 7 or 8 in which said Novolac addition is performed aftersufficient refluxing is effected for substantially complete reaction ofthe resol aldehyde.
 10. The process of claim 8 in which said Novolac isadded prior to initiation of said water removal from said resin solutionor suspension.
 11. The process of claim 8 in which said Novolac is addedprior to removal of 25 percent of the water in said resol resin solutionor suspension.
 12. The process of claim 8 in which said Novolac issubstantially completely free of water prior to said addition.
 13. Theprocess of claim 8 in which at least 35 percent by weight of the waterinitially present in said Novolac preparation is removed prior to saidaddition.
 14. The process of claim 2 in which the carbonaceous filler isfinely divided graphite and said moldable composition contains 35-65percent by weight of said finely divided graphite.
 15. The process ofclaim 8 in which the carbonaceous filler is finely divided graphite andsaid moldable composition contains 35-65 percent by weight of saidfinely divided graphite.
 16. The process of claim 12 in which thecarbonaceous filler is finely divided graphite and said moldablecomposition contains 35-65 percent by weight of said finely dividedgraphite.
 17. The process of claim 4 in which said molded product is aplate having a thickness of 0.04-0.05 inch.
 18. The process of claim 17in which said molding is effected at a pressure of 800 to 1500 poundsper square inch.
 19. The process of claim 18 in which the ratio of partsby weight of said resol resin to parts by weight of said Novolac is inthe range of 70/30 to 50/50.
 20. The process of claim 19 in which saidfinal temperature is at least 2000° F.
 21. The process of claim 19 inwhich said final temperature is at least 3000° F.
 22. The process ofclaim 19 in which said resultant molded product is heated gradually upto a temperature of 600°-700° F. with the temperature increased at arate of 105° F. per hour, then above the range of 600°-700° F. at anincreasing rate of 10°-15° F. per hour up to 800°-850° F. and thereafterat 20°-25° F. per hour up to a final temperature of 1800°-3000° F.,which final temperature is held for at least 24 hours.
 23. The processof any of claims 1, 2, 3, 4, 5, 6, 7, 11, 13 or 15 in which said moldingis effected at a pressure of 800-1500 pounds per square inch.
 24. Theprocess of claim 15 in which said hexamethylenetetramine is used in aproportion of 1 to 5 percent by weight based on the weight of resinproduct.
 25. The process of claim 14 in which said Novolac resin isadded prior to the removal of 50 percent of the removable water fromsaid resol resin solution or suspension.
 26. The process of claim 25 inwhich said amine is hexamethylenetetramine, the phenol component in bothsaid Novolac and said resol resins is phenol and the aldehyde in saidresol resin is formaldehyde.
 27. The process of claim 26 in which thefurfuraldehyde is at least 75 molar percent of the aldehyde component.28. The process of claim 14 in which said Novolac resin is added priorto the removal of 75 percent of the removable water from said resolresin solution or suspension.
 29. The process of claim 28 in which saidamine is hexamethylenetetramine, the phenol component in both saidNovolac and said resol resins is phenol and the aldehyde in said resolresin is formaldehyde.
 30. The process of claim 29 in which thefurfuraldehyde is approximately 100 molar percent of the aldehydecomponent.
 31. The process of claim 30 in which the amount of graphiteis 40-60 percent by weight of the total moldable composition.